US Government Data.
Data.gov API is a free Government API that requires apiKey authentication, is served over HTTPS and has unconfirmed CORS support.

Unified API suite · now live
Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Contains live datasets including information about petitions, bills, MP votes, attendance and more
This API provides read access to DIP entities (e.g. activities, persons, printed material)
Yes. The Data.gov API is listed in the Government category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
Yes. The Data.gov API uses apiKey authentication, so you need to register for credentials before making requests.
CORS support for the Data.gov API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Data.gov API is served over HTTPS, so it's safe to use in production.